Lead-acid batteries include a plurality of interleaved positive and negative battery plates, each composed of a lead alloy grid and electro-chemically active leaded paste applied to the grid. Lead-acid battery grids have a plurality of spaced apart and transversely extending wires or wire segments to define a reticulated grid having open spaces between the wire segments. The grids are usually “over pasted” so that the wire segments are embedded in and surrounded by the paste, and the paste fills the open spaces between the wire segments. The wire segments of the battery grids are of varying cross-section and are sufficiently spaced apart so that the open spaces between the wire segments comprise a majority of the surface area of the expansive plane of the grids.
Prior continuous grid manufacturing techniques yielded grids having relatively smooth surfaces. For example, battery grids may be manufactured by continuously casting molten lead around a rotating cylindrical drum having a battery grid cavity formed in the drum's outer surface. The molten lead is pressurized and directed to successive segments of the drum's outer surface through an orifice in a fixed shoe, which has a curved surface in close, conforming, and sliding engagement with the drum's outer surface.
Continuous grid casting processes usually produce battery grids having lead wire segments W of generally trapezoidal cross section, as shown in FIG. 19. The trapezoidal wire segments W are generally narrower at their lower ends L in the bottom of the drum cavity and are generally wider at their upper ends V at the drum's outer surface. The differential in width and a difference in temperature between the drum and the relatively hotter shoe causes the cast lead wire segments W to cool faster at the narrower lower ends L and slower at the wider upper ends V. The differential in cooling yields smaller average grain size at the narrower lower ends L and larger average grain size at the wider upper ends V, and sufficient but relatively low tensile strength. While inconsistencies in grain size of the lead and in wire shape may be tolerable for use in negative battery grids, they result in positive battery grids that tend to corrode quickly and have relatively short lives in lead-acid batteries.